One of the applications of the invention seeks to read a mold number written a portion of the outer side wall of a container, e.g. on the insweep of a bottle, in particular a glass bottle. In certain circumstances, this number is written in the form of a code made up of portions in relief, e.g. beads, formed on the insweep (or “heel”), i.e. the bottom end of the side wall of the container. In this context, it is important to identify the positions of these portions in relief, in particular their angular positions, in order to be able to deduce therefrom the code and thus the mold number.
In the preferred field of application of the invention, it is known to read a mold number carried by containers, e.g. in order to associate potential defects as may be detected by dedicated sensors with the number of the defective mold. It is thus possible for containers fabricated by a defective mold to be rejected automatically. Reading an identification code can also make it possible to take containers coming from one or more molds automatically, in particular for sampling purposes. The subject matter of the invention thus also finds another advantageous application in the field of sorting empty or full containers by mold number. Various devices have already been proposed in the prior art. Some of those devices require the container to be pivoted about its central axis in front of a reader device, and they are thus complicated, and they also slow down conveyor operations.
Document EP 1 010 126 describes a method of optically reading portions in relief forming an identification code. In the method described in that document, provision is made to light the portion of interest of the outer side wall of the container, which portion is limited along the direction of an installation axis but extends over 360° around the installation axis. In an example, the insweep of a glass bottle is lit in that way. The lighting is performed using a light source that provides a peripheral incident light beam having radial light rays contained in a radial plane containing the installation axis. The radial rays are directed towards the installation axis and the beam as generated in this way comprises non-parallel radial rays in a common radial plane. The method described in that document makes provision for using an optical element, specifically a concave frustoconical mirror flaring downwards away from an installation zone in which the container for observation is placed, to form a plane image of the portion of interest of the wall of the container. An optical system is used to form this image in the field of view of a matrix photoelectric sensor. The method then includes the step of processing the image received by the sensor in order to detect the portions in relief in order to be able to decode the identification code.
In order to perform that method, Document EP 1 010 126 describes a device that is contained entirely below the installation zone of the container and that includes a lighting system, e.g. using an annular optical fiber, for delivering an incident light cone serving to light the entire periphery of the insweep of the container. The device also has a matrix camera, i.e. a camera capable of recovering two-dimensional images, for the purpose of receiving the image of the portion of interest of the outside surface of the container. An optical system is interposed between the installation zone and the sensor in order to form an image on the sensor of the portion of interest of the outer side wall of the container. The optical system has an optical element constituted by a circularly symmetrical frustoconical optical mirror. The optical system also has a standard objective lens incorporated in the matrix camera and a deflection mirror arranged at 45° relative to an installation axis corresponding both to the central axis of the incident light source and to the central axis of the optical element. The camera can thus be placed at 90° relative to the installation axis in order to reduce the overall size of the device along the direction of that axis. The optical system, taken overall between the sensor and the installation zone for receiving a container for observation can thus be said to present an optical axis made up of two mutually-orthogonal main portions: one beside the camera, and the other beside the installation zone. The advantage of the device described in that document lies in the fact that the lighting system, the sensor, and the optical system are arranged below the installation zone that is to receive a container for observation, the installation zone being the observation zone of the device. As a result, it is possible to move the container perpendicularly to its central axis in order to bring it into the installation zone. Such a device is thus easily installed below a line for conveying bottles or containers without interfering with the movement of the containers, it being understood that as a general rule container conveyor systems move containers along a travel path that is perpendicular to the axis of their central axes.
The device described in Document EP 1 010 126 is thus particularly suitable for reading portions in relief carried on the side wall of a container without requiring any element of the device to be at the same height as the portion of interest on the side wall where it is desired to read such portions in relief. Furthermore, by means of its lighting and peripheral vision system, making it possible to observe 360° around the axis of the container, that device and that method do not require the container or the reader device to be set into rotation.
It can be understood that the device and the method described in Document EP 1 010 126 make use of the fact that the incident light beam is reflected at least in part by specular reflection on the portion of interest of the outer side wall of the container and on its portions in relief.
That device is entirely satisfactory in most application situations. Nevertheless, under certain circumstances, it has been found that that device and that method need to be modified in order to read portions in relief under certain conditions. Specifically, depending on the shape of the outer side wall and as a function of the shape of the portions in relief carried on that surface, circumstances can exist in which the optical system of the sensor can no longer distinguish light rays reflected by the portions in relief from rays reflected by the remainder of the insweep. With that device, it is possible to adjust the angle observation each time there is a change of article being fabricated, but to do that it is necessary to change the optical element and thus to have a wide range of conical observation mirrors presenting different geometrical characteristics. Unfortunately, such mirrors are expensive, and changing mirrors is a manual operation that pointlessly lengthens the time needed for adjustment, which is not satisfactory from an operational point of view. Furthermore, such adjustment by changing mirrors does not enable the operator to observe in real time the effects of the change by monitoring the result of the change as produced in the image. In certain circumstances, the operator wastes time selecting the best conical mirror from a range. Finally, adjustment by means of a range of parts allows for a limited number only of configurations.